The fastening of the extremity of a pipe to a hydraulic connection terminal body, fitting the extremity onto an internal cylindrical element, then pressing the pipe on said element by means of radial deformation of an external sleeve is known.
If the pipe is made in a pliable material, such as a plastic material, the use of an internal element generally cylindrical is known whose external surface has successive ridges and ring-like grooves. The pressure of the pipe on this sleeve deforms the material of the pipe making said ridges penetrate into the material itself, with effective hydraulic seal action.
When the fitting is intended to receive rigid or semi-rigid pipes, in plastic, metal or multi-layer metal and plastic, a problem is constituted by the need to achieve efficient resistance both to the withdrawal mechanical stress and to the hydraulic leakages, which is also reliable over its service life. The deformation of the external sleeve proves to be easier and can be deeper, if it is carried out in correspondence with discrete circumferential areas, so as to form deformed ring areas to assume a reduced diameter.
The present invention therefore concerns that type of fitting in which the whole section of the rigid or semirigid pipe is deformed because the pipe follows the path of the internal sleeve that is not generically cylindrical, but has at least one section with a heavily reduced diameter into which the pipe is forced to penetrate by deformation of its entire section, in the sense of reducing the diameter.
According to the known technique, in this type of fitting the internal element is fitted with circumferential grooves corresponding in position to the areas of the sleeve that are intended to be deformed. The deformation of the pipe, so that it takes on such a path that adheres to the internal element also in the areas with reduced diameter is obtained by means of deformation of an external sleeve fitted onto the pipe. The sleeve is deformed by means of a semi-circular jaw clamp with configuration corresponding to that of the sleeve, fitted with protruding circumferential beads, to compress and selectively deform the desired areas of the sleeve, in correspondence of the areas of the pipe that have to be deformed with diameter reduction to penetrate the reduced diameter areas of the internal element.
With such a known configuration of parts, between internal element and sleeve a winding path seat is formed within which the pipe is received and pressed, with good resistance to withdrawal, because of the deep deformation to which the diameter of the pipe itself is subject in limited areas.
Joints of the type described are known in numerous variants, and are for example shown in U.S. Pat. No. 5,829,795.
A serious inconvenience that is presented by this type of pressure joint known is constituted by the fact that their reliability is determined by the precision with which the sleeve pressed, in relation the configuration the internal element onto which the pipe is fitted.
In fact the beads of the deformation collet of the sleeve are required to act in correspondence with the grooves of the internal element, to obtain the desired effect.
Nevertheless, the application of these fittings to the extremity of a pipe can also be carried out in the formation of plants on the installation site and therefore not in the workshop where the operator can work at ease. In awkward conditions it may happen that the operator does not apply the tightening jaws in axially correct position on the external sleeve so that it is deformed in axially incorrect positions, and the grooves formed in the sleeve by the beads of the jaws do not correspond with sufficient precision to the grooves of the internal element, seriously compromising the formation of the joint, without the possibility of successive corrections of the incorrect deformation.
Proposal has also been made to define the sleeve areas that are subject to maximum pressure by a deformation collet by making slight protrusions on the external surface of the sleeve situated in correspondence of areas where maximum pressure on the pipe is required, to push it against a corresponding area of the internal element, as shown in DE 101 37 078. In this manner the result is that there are areas of the pipe that are more compressed so that the plastic material that constitutes the wall of the pipe, or at least its external layer, is deformed locally altering the thickness of the pipe and causing the insertion of the material in said seats for elastic gaskets of a generically cylindrical internal element of the fitting. The requirement in this document is that excessive diametric deformation of the pipe is avoided so as not to damage elastic gasket elements, while according to the aims of the invention the contrary is required, that is that the pipe is deeply deformed in the sense of locally diminishing its diameter, to reach a winding path that adapts to an internal element that has wide and deep grooves, to anchor mechanically against withdrawal.